Potassium ferrooxalate, also known as potassium bisoxalatoferrate(II), is a salt with the formula K
2], sometimes abbreviated K
2. The ferrooxalate anion (negative ion) [Fe(C
is a transition metal complex, consisting of an atom of iron in the +2 oxidation state bound to two bidentate oxalate ions C
4. The anion charge is balanced by two cations (positive ions) of potassium K+
Potassium iron(II) oxalate
3D model (JSmol)
|Appearance||orange-yellow solid (anhydrous), golden-yellow crystals (dihydrate) |
|Melting point||decomposes at 470 °C |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Potassium ferrooxalate is believed to be formed when the related compound potassium ferrioxalate K
3] is decomposed by light in solution (a common method of actinometry) or heated above 296 °C.
While the ferrooxalate anion had been previously identified in solution, the solid salt was described only in 1992, by J. Ladriere. He obtained it by dissolving the approriate amounts of potassium oxalate dihydrate K
2O and iron(II) oxalate dihydrate FeC
2O in boiling water, partially evaporating the red solution, and cooling it to room temperature, when gold-yellow crystals of K2Fe(ox)2·2H
2O precipitated. (The whole procedure should be performed in an oxygen-free atmosphere to avoid oxidation of the Fe2+
core to Fe3+
The dihydrate loses two water molecules at 200 °C.
The anhydrous salt is stable in the absence of oxygen up to about 470 °C, when it decomposes into potassium oxalate and ferrous oxide FeO (which disproportionates partly into magnetite Fe
4, metallic iron, and cementite Fe